This invention relates to a test apparatus for testing the size of restrictions for air or gas flow and, more particularly, to such a test apparatus which ignore non-linearities caused by system and variable atmospheric conditions.
Prior art test apparatus, which are used for testing the size of restrictions, tend to be non-linear and dependent upon such variable conditions as temperature, pressure and circuit non-linearities. Even when the manufacturer of the test equipment states that its equipment is linear, the system really is not because the test apparatus has not been designed to ignore such non-linearities. Other test apparatus requires the use of rather bulky ring standards which, in cooperation with a probe connected to the test apparatus, are used for calibrating the test apparatus. Not only is the test apparatus bulky but these systems are limited because of the use of a probe. The test apparatus according to the instant invention is designed to be simple in construction and ignore non-linearities of the test apparatus and drifting of the output signals due to such variable atmospheric conditions as temperature and pressure.